JP4452696B2 - Method for producing high-strength aluminum alloy material for automobile headrest frame with improved workability - Google Patents

Description

  The present invention relates to a high-strength aluminum alloy material that improves workability and prevents cracking during bending, a method for manufacturing the same, and a headrest frame for an automobile manufactured using the same. More specifically, an Al—Zn—Mg-based aluminum alloy is used as a basic composition, but an aluminum alloy billet in which Mn is added and Zn and Mg are kept within a predetermined range is cast, and this casting is performed. After extruding the billet, the strength is increased by T6 heat treatment, and further, over-aging heat treatment is carried out at a temperature of 170 ° C. to 180 ° C. for 1 hour to 3 hours to perform artificial age hardening. The present invention relates to an improved high-strength aluminum alloy material, a method for manufacturing the same, and a headrest frame for an automobile manufactured using the same.

  In recent years, with the emphasis on labor saving and the importance of environmental preservation, research on lightweight materials that can reduce the weight of transport machines such as aircraft and automobiles has been actively conducted, and aluminum alloys are typically used as lightweight materials. It has been.

  Since aluminum alloys are lightweight and have high specific strength, they are widely used as structural materials and building materials for aircraft, vehicles and the like that require weight reduction and high strength of materials. Recently, aluminum alloys have also been used in small products such as communication equipment, semiconductor and computer electrical / electronic components, leisure goods and some automotive components, and the range of use of these alloys has further expanded. It's getting on.

  Aluminum alloys can be roughly divided into aluminum alloys for casting and aluminum alloys for processing. Further, the aluminum alloy for processing is further mainly composed of a high-strength alloy system mainly composed of duralumin Al-Cu-Mg system and Al-Zn-Mg system, Al-Mn system, and Al-Mg-Si system. It can be broadly divided into corrosion-resistant alloy systems. Furthermore, the aluminum association uses four-digit aluminum alloys ranging from 1000 series to 8000 series, with 2000 series and 7000 series corresponding to high-strength alloy systems.

Recently, research on 7000 series alloys having the highest strength among aluminum alloy series has been actively conducted. This type of alloy is of the Al—Zn—Mg type, and has attracted attention as a high-strength alloy because MgZn ₂ is contained in the alloy and has high age-hardening properties.

  Typical examples of 7000 series alloys include Al7003 and Al7021. These alloys are precipitation-hardening type alloys that cannot obtain high strength properties unless further heat treatment is performed after the extrusion process. It is a heat treatment type alloy system that is included as an essential process. Various heat treatment methods are conceivable depending on the type of aluminum alloy, but the T6 method is usually used for 7000 series alloys. In the T6 heat treatment method, the alloy is heated at a temperature of 400 ° C. to 500 ° C. to form a solid solution, and then rapidly cooled in water. The rapidly cooled alloy is further heated to a temperature of about 120 ° C. for about 24 hours to artificially age. It is a method of curing.

  Age hardening refers to a phenomenon in which a metal material hardens when left at a predetermined temperature for a certain period of time, and when it is hardened even if it is left at room temperature, it does not become hard unless it is heated somewhat. In some cases, hardening at room temperature is called natural aging, and it is called artificial aging when it does not become hard unless it is heated somewhat. Age hardening results from the precipitation phenomenon in which different solids appear as separate phases in one solid.

Aluminum 7000 series alloys increase in strength by increasing the contents of Mg and Zn and subjecting them to artificial age hardening so that MgZn ₂ is precipitated, but at the same time, they are resistant to grain boundary brittleness and grain boundary stress corrosion. Resistance becomes low. The atomic ratio of Zn / Mg is about 2 to 2.5, but the Zn content is usually in the range of about 3 to 7.5% by weight, and the Mg content is the quantitative reaction level of MgZn ₂ Alternatively, the Zn content is set to be slightly higher. This is because Mg and Zn are not so different in terms of the effect of solid solution strengthening, and in an alloy with an excessive amount of Mg, Al ₃ Mg ₂ that can appear depending on the heat treatment conditions is extremely harmful to stress corrosion.

  As described above, aluminum is manufactured and used in various alloy forms. In particular, 7000 series alloys are mainly composed of Mg and Zn and other transition elements in order to have high strength characteristics. Is used for parts that require high strength properties instead of high-weight steel materials.

  Hereinafter, a process of producing a predetermined product using an ordinary aluminum 7000 series alloy will be described. First, an aluminum alloy billet is cast containing various transition elements in proportions suitable for characteristics, the cast billet is extruded into a predetermined product shape, and then heat-treated by T6 (that is, after solid solution treatment) A predetermined product with high strength is obtained by applying artificial age hardening. Further, after the extruded product is subjected to a solid solution treatment according to the size and desired accuracy of the product, the accuracy is further improved by performing a drawing process, and then an accurate age product is obtained by artificial aging curing.

  In addition to these, in order to obtain various products, it is necessary to bend the aluminum alloy, but the aluminum 7000 series alloys developed so far have improved strength characteristics. On the other hand, since the elongation rate is low and the brittleness is high, there are problems such as cracking and fracture when the bending process is performed. As described above, this is caused by Mg and Zn added for improving the strength characteristics, but in order to eliminate this, a small amount of Cr or Mn is added to the 7000 series alloy to increase the elongation. The method is used. However, this method is limited to the extent that it suppresses natural cracks against stress corrosion of 7000 series alloys, and the problem of generation of cracks during bending is still a problem.

  The main alloy components Mn, Mg and Zn of the 7000 series aluminum alloy excluding a small amount of other alloy components are Mn: 0.1% by weight or less, Mg: 1.2-1 in the case of a conventional Al7021 alloy. 8% by weight, Zn: 5 to 6% by weight. However, in this case, since the content of Mn is 0.1% by weight or less, it is common to produce a billet without containing Mn at the time of casting an aluminum alloy billet. Because it is extremely slight, it remains only to suppress natural cracks. For this reason, in the case of the Al7021 alloy, cracks are generated at the time of bending due to the low stretching ratio, despite the high tensile strength. In order to solve this, Mn is added for the purpose of increasing the stretch ratio, but it is difficult to find a suitable component ratio of Mn, and it is difficult to suppress cracks during bending. There was a problem that.

  Because of this situation, 7000 series high-strength aluminum alloys cannot be freely used for various products, and have been used only for some parts of automobiles that require high strength. This entails significant limitations on the wide range of use of aluminum.

  Of some parts of the automobile, for example, a headrest will be described. The headrest plays the role of protecting the driver's and passenger's heads from impacts in the event of a vehicle collision, and is mounted on the vehicle seat by a headrest frame. Since the headrest frame is required to have high strength in order to avoid deformation and the like even in the event of a vehicle collision, the headrest frame is currently made of steel. However, in order to reduce the weight of the vehicle, it is preferable to manufacture it from a high-strength aluminum alloy material. However, in the case of a high-strength aluminum alloy, as described above, the headrest of the vehicle is caused by problems such as cracking when bent. Could not be applied to the frame.

  Therefore, the present invention has been made in view of the above circumstances, and the object thereof is based on an Al—Zn—Mg based aluminum alloy, in which Mn is added, and Zn and Mg are predetermined. Cast aluminum alloy billet kept in the range of, and after extruding the cast billet to increase the strength by T6 heat treatment, artificial age hardening at a temperature of 170 ° C to 180 ° C for 1 hour to 3 hours The present invention provides a high-strength aluminum alloy material with improved workability that does not cause cracking during bending by further performing the overaging heat treatment, and a method for producing the same.

  Furthermore, another object of the present invention is to provide a headrest frame for automobiles obtained by bending the aluminum alloy material.

  In order to achieve such an object, the present invention provides Si: 0.1 wt% or less, Fe: 0.2 wt% or less, Cu: 0.07 to 0.15 wt%, Mn: 0.1 to 0.00. 15 wt%, Mg: 1.2-1.3 wt%, Cr: 0.07-0.12 wt%, Zn: 5.7-5.9 wt%, Ti: 0.015-0.04 wt% %, Unavoidable impurities: a step of casting an aluminum alloy containing 0.15% by weight or less and the balance of Al into a billet, and a step of extruding the cast billet into a predetermined shape to obtain an extrudate And a T6 heat treatment stage in which the extrudate is subjected to solid solution treatment and then subjected to artificial age hardening, and an overaging heat treatment stage in which the extrudate is subjected to artificial age hardening at a temperature of 170 ° C. to 180 ° C. for 1 hour to 3 hours. High-strength aluminum with improved workability To provide a process for the production of Umm alloy material.

  Further, in the T6 heat treatment stage, when a drawing operation is performed in accordance with a predetermined product shape between the solid solution treatment process and the artificial age hardening process of the extrudate, the drawing ratio is set to 4%. A method for producing a high-strength aluminum alloy material with improved workability is provided.

  Furthermore, a high-strength aluminum alloy material with improved workability manufactured by the above manufacturing method and a headrest frame for an automobile manufactured using the same are provided.

  According to the present invention, an Al-Zn-Mg-based aluminum alloy is used as a basic composition. An aluminum alloy billet in which Mn is added and Zn and Mg are kept within a predetermined range is cast. After extruding the cast billet by T6 heat treatment, it is further subjected to an overaging heat treatment in which it is artificially age hardened at a temperature of 170 ° C. to 180 ° C. for 1 hour to 3 hours. By providing a high-strength aluminum alloy material with improved workability that does not crack, and a method for manufacturing the same, and by providing a headrest frame for automobiles manufactured using the same, a high-strength aluminum alloy material is provided. High-strength aluminum alloys can be applied to products that require various types of bending, such as automotive parts. Increase can both, so that the effect of preventing the labor and environmental pollution can be obtained.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, if it is recognized that a specific description relating to a related known configuration or function may obscure the gist of the present invention, a detailed description thereof will be omitted.

  The present invention is based on the conventional Al-Zn-Mg alloy Al7021, but with the addition of Mn as a transition element to improve the elongation and Mg and Mg to achieve both strength and workability. The Zn content is limited to a certain range within the basic component ratio of the Al—Zn—Mg alloy, and in the heat treatment method, an overage artificial age hardening process is further added to the conventional T6 heat treatment method. And

  First, characteristics related to the component ratio of main transition elements according to the present invention will be described.

  As described in the background art section, main alloy components Mn, Mg, and Zn of a 7000 series aluminum alloy excluding a small amount of other alloy components are Mn: 0.1 in the case of a conventional Al7021 alloy. It is contained at a component ratio of not more than wt%, Mg: 1.2 to 1.8 wt%, Zn: 5 to 6 wt%. The physical property values announced by the Aluminum Association are a tensile strength of about 420 MPa and a stretch ratio of about 13%. For this reason, in the case of the Al7021 alloy, cracks are generated during the bending process due to the low stretch ratio despite the high tensile strength.

  In the present invention, Mn is further added to the aluminum alloy during billet casting to increase the elongation. The transition element Mn spheroidizes the particles in the alloy and contributes to the improvement of the elongation rate. However, when the component ratio increases, the workability decreases and the mold or the processing machine is worn. For this reason, the component ratio of Mn according to the present invention is 0.1 to 0.15% by weight, that is, the elongation is increased, but it is within a range not affecting the workability.

Table 1 below shows that when Mn is further added in an amount of 0.1 to 0.15% by weight in accordance with the present invention, the tensile strength remains unchanged as compared with the conventional Al7021 alloy, but the stretch ratio is improved. Show.

The component ratio of Zn and Mg according to the present invention will be described. Zn and Mg are transition elements that contribute to the strength of the alloy, and are contained for the purpose of increasing the strength. However, an increase in the Mg component promotes a hardening phenomenon at the time of processing the alloy, so that workability is lowered, and extrusion may be impossible depending on the size and shape of the product. In order to prevent this, the aluminum alloy according to the present invention has the Mg component ratio minimized to 1.2 to 1.3% by weight. Further, Zn is preferably maximized from the viewpoint of the strength of the alloy. However, when the component ratio is 6% by weight or more, as a result of the test, cracking occurs during bending. This is because Zn is bonded to Mg to form MgZn ₂ , but Zn remaining unbonded with Mg is present as an impurity in the alloy, which is considered to cause cracks. For this reason, the component ratio of Zn is less than 6% by weight, preferably 5.7 to 5.9% by weight in the upper range.

  FIG. 1 is a cross-sectional view showing the crystal structure of an aluminum alloy when the Zn component ratio is 6% by weight or more and 5.9% by weight or less. According to FIG. 1, in the case of an aluminum alloy with Zn of 5.9% by weight or less according to the present invention, the structure is uniformly formed, and in the case of an aluminum alloy with Zn of 6% by weight or more, the sense of structure varies. There is.

  In short, the main alloy components Mn, Mg, and Zn, excluding the component ratio of a small amount of other transition elements, contain 0.1 to 0.15% by weight of Mn compared to the component ratio of Al7021 alloy. Mg is 1.2 to 1.3% by weight of the lower range, and Zn is 5.7 to 5.9% by weight of the upper range.

  Thus, according to a preferred embodiment of the present invention, the cast billet for the aluminum alloy whose workability is improved during the bending process is Si: 0.1 wt% or less, Fe: 0.2 wt% or less, Cu: 0.07 to 0.15 wt%, Mn: 0.1 to 0.15 wt%, Mg: 1.2 to 1.3 wt%, Cr: 0.07 to 0.12 wt%, Zn: 5. 7 to 5.9% by weight, Ti: 0.015 to 0.04% by weight, inevitable impurities: 0.15% by weight or less, with the balance being made of Al.

  Next, characteristics of the heat treatment process of the present invention will be described.

  When an aluminum alloy as described above is subjected to the conventional T6 heat treatment for increasing the tensile strength by precipitation hardening (that is, the aluminum alloy is rapidly cooled in water after forming a solid solution, and further at a temperature of about 120 ° C. for about 24 hours. When heated and artificially age hardened), an increase in tensile strength due to heat treatment and an improvement in elongation due to the addition of Mn can be obtained, but cracking occurs during bending. In particular, as a result of the test, in the case of an aluminum alloy product of a cylindrical bar having a component ratio according to the present invention, cracks occurred at the bent portion during U-bending. In addition, the rate of occurrence of cracks was significantly higher in the bent product by press bending in which impact was applied to the cylindrical bar than in the bent product by roll bending.

  This is because even if the elongation ratio is increased by adjusting the component ratio of the aluminum alloy for bending, the cylindrical bar is still vulnerable to impacts such as pressing, and as a result, cracks occur during bending. It can be seen. The results of comparison of impact strength by heat treatment are shown in Table 2 below.

  For this reason, in the heat treatment method according to the present invention, after the T6 heat treatment, that is, after heating for about 24 hours at a temperature of about 120 ° C. and artificial age hardening, it is further performed at a temperature of about 170 to 180 ° C. for 1 hour to Heated for 3 hours to cause overaging. As a result of this over-aging hardening heat treatment process, the grain structure of the aluminum alloy becomes coarse, impact energy from the outside cannot be transmitted quickly to adjacent grain boundaries, and the impact energy absorption rate at each grain boundary increases. The impact energy is absorbed inside, and the generation of cracks is suppressed.

Table 2 below shows the component compositions of the aluminum alloy having the component ratio according to the present invention and the main alloy components of the conventional Al7021 alloy for comparison of heat treatment methods. Table 3 below shows aluminum alloys that were heat-treated by the heat treatment method according to the present invention, aluminum alloys that were heat-treated by the T6 heat treatment method, and conventional 7000 series aluminum alloys. The physical property values and the absorption rate of impact energy are shown in comparison.

  As is apparent from Table 3 above, in the case of the specimen 1 subjected to the overaging heat treatment according to the present invention, the elongation ratio was compared with the case of the specimen 2 obtained by subjecting the aluminum alloy according to the present invention to the conventional T6 heat treatment. There is no significant change, and the tensile strength is slightly reduced, but the amount of impact energy absorbed is greatly increased. Moreover, when compared with the conventional Al7021 alloy, the tensile strength was slightly reduced, but both the stretch ratio and the impact energy absorption ratio were significantly improved. In short, the tensile strength is slightly reduced and the amount of impact energy absorbed is greatly increased, so that the aluminum alloy manufactured according to the present invention is a high-strength aluminum alloy and has the property that it does not crack during bending. Have.

  Furthermore, in the overaging heat treatment method according to the present invention, the heating temperature is 170 to 180 ° C., which is a result of the test that the grain boundary is changed so that the size of the internal crystal structure of the alloy is changed to be strong against impact. This is because the heating temperature must be 170 ° C. or higher in order for the film to become coarse. On the other hand, when the heating temperature exceeds 180 ° C., the absorbed amount of impact energy increases, but the tensile strength and the draw ratio are rapidly decreased, so that the high strength characteristics that are the properties of the 7000 series alloy cannot be maintained. In the overaging heat treatment method according to the present invention, the heating time is 1 to 3 hours. This is in order to sufficiently change the crystal structure to the inside of the alloy when heated at a temperature of 170 to 180 ° C. This is because heating time of 1 hour or more is required. On the other hand, as the heating time is extended, the tensile strength and the drawing ratio are reduced, so that the high strength characteristics of the alloy cannot be maintained when heated for 3 hours or more.

  On the other hand, in the heat treatment method according to the present invention, after the T6 heat treatment, that is, after the solid solution treatment, it may be heated at about 120 ° C. for about 24 hours to be subjected to artificial age hardening, and then an overaging heat treatment may be performed. After the solid solution treatment, the heat treatment time may be shortened by heating at about 120 ° C. for about 20 hours to cause artificial age hardening and then performing an overaging heat treatment.

  FIG. 2 is a flowchart schematically showing a manufacturing process of a high-strength aluminum alloy material with improved workability according to the present invention.

  First, an aluminum alloy billet according to the present invention is cast (S01) and extruded in accordance with the shape of a predetermined product (S02), followed by T6 heat treatment, that is, solid solution treatment (S03) and artificial age hardening treatment (S05). Do. At this time, depending on the size and accuracy of the product, a drawing (S04) process is performed after the solid solution treatment (S03) as necessary. This is because when the dimensional accuracy and the target tolerance cannot be maintained only by the shape of the extrusion, the product shape with high accuracy can be obtained by performing the drawing process again. After passing through the process of drawing (S04) and artificial age hardening (S05) in this way, the overage hardening (S06) according to the present invention is performed, and a predetermined bending process (S07) is performed according to the target product.

  When the drawing (S04) process according to the embodiment of the present invention is performed, the drawing affects the tensile strength and the drawing rate of the aluminum alloy, which will be described.

  Drawing is a kind of cold working, and when cold working is performed on metal, work hardening phenomenon due to cold working occurs, resulting in an improvement in strength. However, there are disadvantages such as a reduction in the stretching ratio, and there is a risk of cracking during bending.

For this reason, in performing the drawing process, the drawing ratio, which is the reduction ratio of the sectional area after drawing to the sectional area before drawing, becomes an important factor in relation to the physical property values after drawing. As a result of the test, when the drawing ratio according to the present invention is set to 4%, it is possible to prevent the stretching ratio from being significantly reduced. The drawing ratio test was conducted on a cylindrical bar having a diameter of 10 mm. Table 4 below shows changes in the tensile strength and the drawing ratio depending on the drawing ratios. From this, it can be seen that when the drawing ratio is 4%, the strength increases beyond a predetermined range, and furthermore, it is possible to maintain a drawing ratio that does not cause cracks during bending.

  As is clear from Table 4 above, the tensile strength increases as the drawing ratio increases, and the drawing ratio decreases. However, when the drawing ratio is 4% or more, the drawing ratio decreases rapidly. It is preferable to perform the drawing process while keeping the percentage.

  Accordingly, the extruded product obtained by extruding the aluminum alloy billet into a predetermined product (S02) is more accurately reduced in accordance with the drawing ratio of 4% during the drawing (S04) process. .

  FIG. 3 is a perspective view showing an example of a headrest frame for an automobile manufactured according to an embodiment of the present invention.

  The headrest 10 for an automobile supports the driver's and passengers 'necks to provide relaxation to the driver and passengers, and at the same time absorbs shocks to the driver's and passengers' heads when an accident occurs. Fulfill.

  The headrest 10 is formed of an elastic material and is assembled to the upper end of the backrest 40 of the automobile seat to support the passenger's neck. In addition, a headrest frame 20 that holds the headrest 10 is inserted into the headrest 10, and both end portions of the headrest frame 20 are fitted into two engagement holes 30 that are formed in the upper end of the seat back 40. Thus, the headrest 10 is assembled to the seat in a freely detachable manner.

  The headrest frame 20 is formed by bending a cylindrical bar twice in the same direction into a “U” shape, and both ends of the headrest frame 20 are fitted into both locking holes 30 at the upper end of the seat back and bent. The center portion of the cylindrical bar thus formed is inserted into the headrest 10 to hold the headrest 10.

  A headrest frame 20 according to a preferred embodiment of the present invention is made of a high-strength aluminum alloy material manufactured according to the manufacturing process shown in FIG. 2, and is formed by bending a cylindrical bar-type aluminum alloy material twice. For this reason, while maintaining the same strength as the steel-made headrest frame conventionally used in automobiles, it is lighter than that.

  The headrest frame 20 according to the present invention can also be manufactured by bending a hollow cylindrical pipe-type aluminum alloy material twice.

  4A and 4B are perspective views showing an example of a headrest frame according to an embodiment of the present invention.

  FIG. 4A shows a structure in which the holding force of the headrest frame 21 with respect to the headrest is reinforced by attaching a “T” -shaped plate 22 to the upper center of the “U” -shaped headrest frame 21 similar to FIG. 3. Show.

  FIG. 4B shows the headrest with respect to the headrest by further bending the central portion of the cylindrical bar bent in a “U” shape twice in a direction perpendicular to the surface formed by the “U” -shaped cylindrical bar as in FIG. The structure which reinforces the retention strength of the flame | frame 23 is shown.

  Since the headrest frame according to the embodiment of the present invention is manufactured from the aluminum alloy material according to the present invention, the headrest frame according to the embodiment of the present invention is manufactured in any conventionally known shape. Is possible.

  The above description is merely illustrative of the technical idea of the present invention, and any person who has ordinary knowledge in the technical field to which the present invention belongs will understand the essential characteristics of the present invention. Various modifications and variations may be made without departing. Therefore, the embodiments disclosed in the present invention are for explaining rather than limiting the technical idea of the present invention, and the scope of the technical idea of the present invention is limited by these embodiments. There is no. The protection scope of the present invention should be construed according to the claims, and all technical ideas within the same scope should be construed as being included in the scope of the present invention.

Sectional drawing which shows the crystal structure of the aluminum alloy in the case where the component ratio of Zn is 6 weight% or more and 5.9 weight% or less. The flowchart which shows simply the manufacturing process of the high intensity | strength aluminum alloy raw material by which workability improved by this invention. The perspective view which shows an example of the headrest frame for motor vehicles manufactured according to one embodiment of this invention. The perspective view which shows an example of the headrest frame by one embodiment of this invention. The perspective view which shows another example of the headrest frame by one embodiment of this invention.

Explanation of symbols

10: Headrest 20: Headrest frame 30: Locking hole 40: Seat back 21: Headrest frame 22: Plate 23: Headrest frame

Claims (4)

Si: 0.1 wt% or less, Fe: 0.2 wt% or less, Cu: 0.07 to 0.15 wt%, Mn: 0.1 to 0.15 wt%, Mg: 1.2 to 1. 3% by weight, Cr: 0.07 to 0.12% by weight, Zn: 5.7 to 5.9% by weight, Ti: 0.015 to 0.04% by weight, unavoidable impurities: 0.15% by weight or less Casting an aluminum alloy containing Al and the balance of Al into a billet;
Extruding the cast billet into a predetermined shape to obtain an extrudate;
A T6 heat treatment step of subjecting the extrudate to a solid solution treatment and then artificial age hardening;
An overaging heat treatment step of artificially age-hardening the extrudate at a temperature of 170 ° C. to 180 ° C. for 1 hour to 3 hours;
A method for producing a high-strength aluminum alloy material for a headrest frame for automobiles with improved workability, comprising: The T6 heat treatment step includes:
2. The processability according to claim 1, wherein the extrudate is subjected to a solid solution treatment, a drawing operation is performed in accordance with a shape of a predetermined product, and then artificial age hardening is performed. Manufacturing method of high-strength aluminum alloy material for headrest frames for automobiles . In the drawing operation,
The high-strength aluminum alloy for headrest frames for automobiles with improved workability according to claim 2, wherein the drawing ratio, which is a reduction ratio of the sectional area after drawing to the sectional area before drawing, is 4 %. Material manufacturing method. In the T6 heat treatment step,
Artificial age hardening process, 1 20 ° C. under characterized in that it is carried out by heating 2 0 hours, according to any one of claims 1 to 3, high strength automotive headrest frame workability is improved Manufacturing method of aluminum alloy material.